1. Field of the Invention
The present invention relates to methods of fabricating buried digit lines. Particularly, the present invention relates to a method of fabricating digit lines that are substantially free of stringers. More particularly, the present invention relates to a method of removing stringers from between the straps, plugs and digit lines of semiconductor devices that include digit lines having widths of less than about 0.25 microns. The present invention also relates to semiconductor devices including buried digit lines that are substantially free of stringers and that have widths of less than about 0.25 microns.
2. Background of Related Art
Conventional semiconductor memory devices typically include an array of memory cells, each of which is in communication with a word line and a digit line. Due to the demand for semiconductor devices of ever-increasing density and ever-decreasing size, the semiconductor industry has sought ways to fabricate smaller, more compactly organized features. Thus, in semiconductor memory devices, the sizes of various features, as well as the spacing therebetween, have decreased. For example, the width of state of the art digit lines has decreased to about 0.25 microns or less. The spacing between adjacent digit lines has similarly decreased to about 0.30 microns or less.
Conventionally, photomask techniques, which typically employ visible to near infrared wavelengths of light, have been used to fabricate the digit lines of semiconductor memory devices. The sizes of features of such photomasks are, however, limited by the wavelengths of electromagnetic radiation employed to define these photomasks. As a result, the sizes and spacing of features defined either directly or indirectly by such photomasks are similarly limited.
Semiconductor memory devices that include digit lines having widths of less than about 0.25 microns and pitches of less than about 0.55 microns have been developed. The semiconductor memory devices, however, are relatively inefficient when compared with semiconductor memory devices having wider digit lines and pitches. The inefficiency of these more compact semiconductor memory devices is due, at least in part, to the potential for electrical shorts between adjacent digit lines. Electrical shorts in semiconductor memory devices with densely packed features may be caused by so-called “stringers” that remain following the definition of digit lines or other electrically conductive components, such as the plugs or straps that may be employed to link a contact to its corresponding digit line. The stringers may extend between adjacent structures or from a first structure to a location undesirably close to an adjacent, second structure. Thus, stringers may create an undesirable electrical path between adjacent digit lines.
Since semiconductor memory devices that include digit lines having widths of about 0.25 microns or less and digit line pitches of about 0.55 microns or less may include stringers that would likely cause electrical shorts between adjacent conductive structures, a significant percentage of the semiconductor memory devices will fail quality control testing. Consequently, fabrication costs are undesirably significantly increased.
Accordingly, there is a need for a method by which semiconductor memory devices that include digit lines with widths of less than about 0.25 microns and digit line pitches of less than about 0.55 microns may be more efficiently fabricated. There is a further need for a method of fabricating semiconductor memory devices of increased feature density which employs conventional techniques and equipment.